The present invention relates to a novel method for the surface treatment of the frame of spectacles.
With the recent diversification of the need for design of spectacles or sunglasses, the liking for frame color has also undergone sophistication. Therefore, to meet such customers"" needs, a technology for delicate modulation of frame color is required.
The hitherto-known technology for the surface treatment of the frame includes not only the plating method using a noble metal but also the ion plating method which comprises sputtering with an ionized titanium compound and the color coating method which comprises plating a substrate in advance and applying an electrodeposition coating of a colored resin, among other methods.
However, when the surface treatment is carried out by these methods, the following problems are encountered.
In the plating method, the kind of color or tone that can be obtained is limited. Moreover, the fine adjustment of tone is extremely difficult. For fine adjustment of tone, such parameters as the plating bath composition, pretreatment conditions, etc. must be strictly controlled but such delicate control is actually difficult. Therefore, it is not easy to faithfully reproduce the same color by the plating method. Furthermore, in order that the surface of only a given portion of the frame may be treated by the plating method, it is necessary to follow a time-consuming procedure comprising a masking step, a plating step, a second masking step, a second plating step, and so on.
In addition, appearance and corrosion resistance considerations require absence of pinholes in the plate formed, but this can be assured only by building up a plurality of plate layers in superim-position. On the other hand, the mere thickening of the plate leads to troubles such as cracking and peeling. Thus, generally the frame of spectacles is subjected to bending or torsional stresses in fitting and the plate layer tends to crack or peel off in the course.
The plating method generally involves a series of treatments, namely racking, cleaning, acid treatment, strike plating, baking and electroplating, which takes time and labor. Moreover, the plating method requires a large volume of liquid as well as violent or toxic chemicals so that a costly waste water treatment facility for safety disposal is required. Furthermore, the sludge treatment is also a cost item and the treatment of waste water calls for stringent control and monitoring by qualified personnel.
Furthermore, when the frame of spectacles is to be treated by the plating method, the plating conditions must be critically controlled according to the kind of frame material used. Should the plating conditions be incompatible, even in the least, with the frame material, the surface of the frame of spectacles would develop the so-called xe2x80x9crough skinxe2x80x9d to detract from the marketability of the end product.
Even in the ion plating method involving a sputtering operation, fine tone control is not easy and a localized surface treatment is also difficult.
Furthermore, a vacuum furnace with a comparatively large built-in heater as well as a high voltage source is required in the ion-plating method. Since the sputtering direction is linear and the shadowed part cannot be colored, it is necessary to install a device for rotating the frame of spectacles internally of the equipment so that an increase in initial cost is inevitable. Furthermore, since the adhesion of the ion plating film is considerably dependent on the degree of cleaning of the base material, a high-precision cleaning equipment is required. Another disadvantage is that since the treating temperature in this method is comparatively high, the method cannot be applied to the frame made of copper alloy which is vulnerable to high temperature.
With the color coating method which is an electrodeposition process, fine tone control is difficult and the localized coloration of the frame is not easy. In addition, the colored resin tends to be swollen by, or partially dissolved in, commercial skin care products, hair tonics, hair dyes, and so forth.
As pointed out above, all of these surface treatment systems are not amenable to fine tone modulation and, in addition, are highly costly. Moreover, there is room for further improvement in the adhesion and sealing power of the coating layer.